The present disclosure relates generally to resist materials, such as can be used in immersion or non-immersion photolithography, or other processes used in the manufacture of semiconductor integrated circuits.
Lithography is a mechanism by which a pattern on a mask is projected onto a substrate such as a semiconductor wafer. In areas such as semiconductor photolithography, it has become necessary to create images on the semiconductor wafer which incorporate minimum feature sizes under a resolution limit or critical dimension (CD). Currently, CDs are reaching 65 nanometers and less.
Semiconductor photolithography typically includes the steps of applying a coating of photoresist (also referred to as resist) on a top surface (e.g., a thin film stack) of a semiconductor wafer and exposing the photoresist to a pattern. The semiconductor wafer is then transferred to a developing chamber to remove the exposed resist, which is soluble to an aqueous developer solution. As a result, a patterned layer of photoresist exists on the top surface of the wafer.
Immersion lithography is a new advance in photolithography, in which the exposure procedure is performed with a liquid filling the space between the surface of the wafer and the lens. Using immersion photolithography, higher numerical apertures can be built than when using lenses in air, resulting in improved resolution. Further, immersion provides enhanced depth-of-focus (DOF) for printing ever smaller features. It is understood that the present disclosure is not limited to immersion lithography, but immersion lithography provides an example of a semiconductor process that can benefit from the invention described in greater detail below.
The immersion exposure step may use de-ionized water or another suitable immersion exposure fluid in the space between the wafer and the lens. Though the exposure time is short, the fluid can cause heretofore unforeseen problems. For example, droplets from the fluid can remain after the process and can adversely affect the patterning, critical dimensions, and other aspects of the resist.
One solution to help reduce defects, such as watermark defects, is to use a top coat layer on the resist layer. One such example is shown in U.S. Pub. No. 2006/111550, which is hereby incorporated by reference. However, the addition of a top coat layer provides additional concerns, and adds an additional layer to the entire process which increases overall production cost.
This application is related to U.S. application Ser. No. 11/324,588 filed Jan. 3, 2006 entitled, “Novel TARC Material for Immersion Watermark Reduction”, which is hereby incorporated by reference.